Abstract
PURPOSE: Individuals who exercise are at lower risk for breast cancer and have better post-diagnosis outcomes. The biological mechanisms behind this association are unclear, but DNA methylation has been suggested. METHODS: We developed a composite measure of DNA methylation across 45 CpG sites on genes selected a priori. We examined the association of this measure to self-reported physical activity and objectively measured cardiovascular fitness in a sample of healthy nonsmoking adults (n = 64) in an exercise promotion intervention. RESULTS: Individuals who were more physically fit and who exercised more minutes per week had lower levels of DNA methylation. Those who increased their minutes of physical activity over 12 months experienced decreases in DNA methylation. CONCLUSIONS: DNA methylation may be a mechanism linking exercise and cancer incidence and could serve as a biomarker for behavioral intervention trials. Studies with larger samples, objectively measured exercise, and more cancer-related markers are needed.